Biology; Chemistry; Physics: Post your doubts here!

[Nabeel.Ahmad]

YOU SHOULD READ BOOK OF ROGER NORRIS OF CAMBRIDGE INTERNATIONAL AS AND A LEVEL....

Okay, sure.

 

[black widow]

So you've got an excellent grasp on all the concepts in Chemistry.

i cant judge it myself

 

[asadalam]

Chemistry is easy enough,especially ATP.I mean i got 58/60 without even studying it before the paper.A few papers are enough to give you the pattern,and its smooth sailing from there.But MCQs prove challenging,while P2 is also pretty easy..

 

[black widow]

Chemistry is easy enough,especially ATP.I mean i got 58/60 without even studying it before the paper.A few papers are enough to give you the pattern,and its smooth sailing from there.But MCQs prove challenging,while P2 is also pretty easy..

the pattern in ATP is the same with the same titration, and rate of reactions questions ending the paper, along with an identification of ions question as well

 

[♣♠ MagneD ♣♠]

Chemistry is easy enough,especially ATP.I mean i got 58/60 without even studying it before the paper.A few papers are enough to give you the pattern,and its smooth sailing from there.But MCQs prove challenging,while P2 is also pretty easy..

39/40 and 53/60 in exams and read whole book in 4 days....@@@!!!

 

[binder]

can anyone give brief description in redox reaction....?????????????

 

[black widow]

can anyone give brief description in redox reaction....?????????????

exactly what in redox reaction?
llke oxidation or reduction or both?

 

[asadalam]

b)second row
Current is divided in parallel so shouldnt it be 4.6,2.3,2.3?

 

[♫Prince Shah♫]

binder
When oxidation and reduction take place simultaneously in a chemical reaction, it is known as REDOX REACTIONS.

For example,

Zn + CuSO4 --> ZnSO4 + Cu

In this reaction Zn gets oxidised and Cu gets reduced. Hence this is an example of Redox reaction.

 

[Nabeel.Ahmad]

b)second row
Current is divided in parallel so shouldnt it be 4.6,2.3,2.3?

But the switch is open. Current won't be divided, i think.

 

[black widow]

b)second row
Current is divided in parallel so shouldnt it be 4.6,2.3,2.3?

the question says that when the switch D is open, the battery supplies a current of 4.6 A, thus we know that for on of the bulb to glow, a current of 4.6 A shud flow through it
when we close the switch, the battery has to supply enough current for both lamps to light, so the answer will be
9.2, 4.6, 4.6

 

[asadalam]

But the switch is open. Current won't be divided, i think.

No its closed.

 

[♫Prince Shah♫]

the question says that when the switch D is open, the battery supplies a current of 4.6 A, thus we know that for on of the bulb to glow, a current of 4.6 A shud flow through it
when we close the switch, the battery has to supply enough current for both lamps to light, so the answer will be
9.2, 4.6, 4.6

i think the same brox..

 

[♫Prince Shah♫]

binder
When the reacting species, capable of losing electrons (reducing agent) and that capable of gaining electrons (oxidizing agent) are present in the same solution a direct redox reaction takes place. In direct redox reactions, the electrons move randomly in all the directions through very short distances. So, in direct redox reactions the net movement of electrons in any direction is zero. The change in chemical energy in such reactions appears as heat.
For example, Oxidation of Zn by Cu2 + .

When a strip of metallic zinc is placed in a solution of CuSO4, after sometime it is noticed that,

• A part of zinc metal plate has dissolved and has lost weight.

• The bluish colour of the solution gradually fades away.

• Reddish metallic copper has started depositing on the zinc plate or is settling down at the bottom of the beaker.

• The presence of Zn2 + ion in the solution may be confirmed by passing H2S gas through the colourless solution after making it ammoniacal by adding ammonia and ammonium chloride when white precipitate of ZnS (zinc sulphide) is formed. The solution remains electrically neutral during and after the reaction.

These observations can be explained as follows:

Solution of copper sulphate contains Cu2 + ( a q ) and SO4 2 - ( a q ) ions. When zinc plate is placed in a solution of copper sulphate, zinc being more electropositive than copper, loses electrons to form Zn2 +ions. The Cu2 + ions gain these electrons to form copper metal. This is displaced as copper metal, a reddish precipitate. As the concentration of Cu2 + ions present in the copper sulphate solution decreases the blue colour of the solution fades away. The overall reaction may be written as:

Electrons are transferred from Zn atom to Cu2 + ion directly. So, this reaction is a direct redox reaction.

Fig: - Displacement of copper from copper sulphate solution by zinc

 

[black widow]

also remember that the oxidation state of an ATOM will always be 0

 

[Nabeel.Ahmad]

also remember that the oxidation state of an ATOM will always be 0

Do Atoms have oxidation states, or elements?

 

[♫Prince Shah♫]

Do Atoms have oxidation states, or elements?

yup..

 

[black widow]

Do Atoms have oxidation states, or elements?

atoms are not stable, they have not formed ions
thus by default, their oxidation state remains 0
do not confuse oxidation states of atoms and elements

and atom is the unstable form of an element
for example Zn is the atom of the element Zn
the ion of the ELEMENT is Zn+2

 

[asadalam]

Do Atoms have oxidation states, or elements?

Oxidation state of an element will be 0.O2 is not an atom but its oxidation state is 0.

 

[♫Prince Shah♫]

yup..

always 0